Stable aqueous glycol solution of
tetracycline aluminum calcium
gluconate complex having a ph of
about



United States Patent 26,541 STABLE AQUEOUS GLYCOL SOLUTION 0FTETRACYCLINE ALUMINUM CALCIUM GLUCONATE COMPLEX HAVING A pH 0F ABOUT 7.5T0 9 Edward Grant Remmers, Ridgewood, and George Madison Sieger,Montvale, N.J., and William Charles Barringer, Pearl River, N.Y.,assignors to American Cyanamid Company, Stamford, Conn., a corporationof Maine No Drawing. Original No. 3,159,542, dated Dec. 1, 1964, Ser.No. 248,231, Dec. 31, 1962. Application for reissue Sept. 29, 1966, Ser.No. 589,163 U.S. Cl. 424227 5 Claims Int. Cl. A6lk 27/00; C07c 103/19Matter enclosed in heavy brackets II] appears in the original patent butforms no part of this reissue specification; matter printed in italicsindicates the additions made by reissue.

This invention relates to novel liquid compositions of tetracycline,which are suitable for parenteral administration. Furthermore, theinvention relates to stable liquid parenteral solutions of tetracyclinealuminum calcium gluconate. These compositions are unique in that theypossess the advantage of stability over a sustained period of time.

A thoroughly stable parenteral composition of tetracycline has beenunavailable, and tetracycline for parenteral use was available only inthe dry form, which required reconstitution immediately prior toadministration. Therefore, although this mode of administration isadequate, the relative merits of the preparation are inhibited by thedisadvantages inherent thereto. The disadvantages primarily reside in,the inconvenience of preparing the solution under adverse circumstances,as well as, the ease with which contamination could occur. Attempts toformulate tetracycline in a stable liquid preparation have not met withsuccess. Formulations have included the use of aqueous propylene glycolas a vehicle and have resulted in preparations which were highlyunstable. Upon dilution of the aforementioned preparations with copiousamounts of water, a precipitate immediately resulted which wassubsequently identified as the antibiotic. Accelerated stability studiesto determine microbiological potency, expressed in milligrams permilliliter of tetracycline present in the preparation, have resulted inascertaining a loss of approximately 85 percent over a three weekperiod, when stored at 37 C.

A particular object of the present invention, therefore, is to provide astable liquid preparation of tetracycline suitable for parenteraladministration. Further objects will become obvious in the light of thefollowing disclosure.

The inventors have discovered that contrary to the statementhercinbefore set forth, a stable liquid composition of tetracycline maybe obtained by the use of the antibiotic metal acid complex, which is anassociation of molecules which are considered as being bound together byresidual valences, dispersed in an aqueous solution containing 3080% ofa physiologically acceptable glycol. The tetracycline metal acid complexwhich is used to obtain the stable liquid compositions of the presentinvention is tetracycline aluminum calcium glu conate, which isdescribed in US. Patent No. 2,736,725. It has been found that when thiscomplex is dissolved in an aqueous solution of a physiologicallyacceptable glycol that a stable, parenterally acceptable solutionresults. Solutions of tetracycline aluminum calcium gluconate complex ina 70 percent propylene glycol solution, for example, at a pH of 8.5.retained 90 to 100 percent of initial potency after acceleratedstability studies at 37 C. for nine weeks and 42 C. for two months. Thestable liquid preparations were found effective in producing ReissuedMar. 11, 1969 high blood levels comparable with blood levels produced byreconstituted aqueous preparations of these complexes, and were foundgenerally quite suitable for parenteral use. A comparison of the stableliquid preparations of the present invention with those which wereheretofore available, illustrates an outstanding improvement. Thepreparations of the present invention do not deteriorate and there is aconcomitant retention of microbiological potency over a sustained periodof time. Therefore, the problems inherent to those preparations whichrequire reconstitution immediately prior to administration are obviatedand preparations having uniform dosage levels are at last realized bythe advent of the solutions of the present invention.

The complex is believed to have the composition of 12 moles of calciumper mole of tetracycline, 3-4 moles of aluminum per mole oftetracycline, and from 6-12 moles of gluconic acid per mole oftetracycline. The addition of more gluconic acid, although it would notaffect the solubility, would serve no practical purpose. These complexesare prepared by known methods as described in US. Patent No. 2,736,725.

The vehicle employed in the present invention is an aqueous solution ofa physiologically acceptable glycol, such as propylene glycol, glycerol,isopropylidene glycerol, and polyethylene glycol. Stable solutions areprepared using concentrations of 30-80 percent of physiologicallyacceptable glycols, the preferred range being between 5075 percent. Whenthe concentration of organic solvent is less than 20 percent, a hazedevelops in the solution, which is not pharmaceutically acceptable forparenteral preparations.

The composition is prepared by dissolving the tetracycline metal acidcomplex in water and then adding the remainder of the vehicle. The finalcomposition is then titrated to a pH of 7.5-9.5 using a basic substance.The neutralizing agents to be used are those which are water soluble andphysiologically acceptable, and have a dissociation constant of greaterthan l0 Among the most useful neutralizing agents are the loweraliphatic amines, such as monoethanolamine, diethanolainine andtriethanolamine.

The composition may also be prepared by formation of the tetracyclinemetal acid complex in situ. However, when aluminum isopropoxide is usedas the source of aluminum ions which is the preferred process, it isnecessary to remove the isopropanol which results as a byproduct in theformation of the complex. The removal of the isopropanol is necessitatedby the fact that isopropanol is not physiologically acceptable.

Of particuar concern in the preparation of stable liquid preparations oftetracycline is the problem of discoloration which may result as aneffect of oxidative degradation. This can be overcome by the addition ofa physiologically acceptable and pharmaceutically compatible antioxidantor by the exclusion of oxygen from the solution while in storage. Theexclusion of oxygen is accomplished by storing the solution under aninert atmosphere, such as nitrogen or other inert non-reactive gases.Various antioxidants may be used such as sodium formaldehydesulfoxylate, ascorbic acid, and sodium, bisulfite, and are employed inantioxidant amounts, which are preferably within the range which issuitable for parenteral preparations, for example sodium formaldehydesulfoxylate is used at a concentration of 0.5-1%.

The preparation may also include local anesthetics, such as procaine andxylocaine, for the purpose of reducing discomfort at the site of theinjection.

Parenteral preparations of broad spectrum antibiotics for the treatmentof humans and animals are usually made available to the doctor andveterinarian in 2 to 4 ml.

dosage units; and may contain anywhere from to 125 mg. of antibiotic perml. depending on the maximum dosage required over any given period.

It will thus be seen that the invention provides a stable liquidpreparation of tetracycline as the metal acid complex, containing 10 to125 mgJml. of tetracycline. The composition of the complex contains from3 to 4 moles of aluminum per mole of tetracycline, from 1 to 2 moles ofcalcium per mole of tetracycline, and from 6 to 12 moles of gluconicacid per mole of tetracycline. Most advantageously the preparation istitrated to a pH of about 7.5 to 9 by the use of a soluble,physiologically acceptable base, this being the pH range whereintetracycline attains its optimum physiological absorption. The wordtetracycline as used in this specification shall include the acidaddition salts of tetracycline, as well as the base.

Stable liquid preparations of either 6-deoxy6-demethyltetracycline,G-demethyltetracycline, o-deoxytetracycline, or7-chloro-6-demethyltetracycline, may be attained by the use of the metalacid complex of said tetracyclines, again employing as the vehicle anaqueous solution of a physiologically acceptable glycol and having a pHof about 7.5 to 9.

The following examples are provided for illustrative purposes and mayinclude particular features of the invention. However, the examplesshould not be construed as limiting the invention, many variations ofwhich are possible without departing from the spirit or scope thereof.

EXAMPLE I Stability of Aqueous Propylene Glycol Solutions ofTetracycline This example illustrates the well-known fact thattetracycline as either the hydrochloride or neutral form is notphysically stable in an aqueous propylene glycol solution.

A composition containing the following ingredients was prepared:

Tetracycline HCl "mg/ml-.. 50 Sodium formaldehyde sulfoxylate -percent0.5 Propylene glycol do 75 Magnesium chloride hexahydrate do 2.5

Ethanolamine, to pH 8.5. Water, q.s. ad 100%.

The composition was then added to a beaker containing distilled water.Immediately upon the addition of the preparation to the beaker ofdistilled water, a precipitate formed. The precipitate was subsequentlyidentified as the antibiotic.

The aforementioned procedure was again followed using the sameformulation but substituting for tetracycline HCl, tetracycline neutral.Upon the addition of this preparation to a beaker containing distilledwater, a precipitate immediately formed, which was subsequentlyidentified as the antibiotic.

Therefore, neither the tetracycline or its acid addition salts arephysically stable in an aqueous propylene glycol formulation.

EXAMPLE II Stability With Regard to Potency of Aqueous Propylene GlycolSolutions of Tetracycline This example demonstrates that tetracycline aseither the hydrochloride or neutral form is not stable with regard topotency in an aqueous propylene glycol solution.

A composition containing the following ingredients was prepared:

Tetracycline HCl mg./ml 45 Sodium formaldehyde sulfoxylate percent 0.5Propylene glycol do 75 Magnesium chloride hexyhydrate do 2.5

Ethanolamine, to pH 8.5. Water, q.s. ad 100%.

The preparation was then subjected to an accelerated stability study fora period of 3 weeks in which said preparation was stored at 37 C. andperiodically analyzed for tetracycline content. The results of thestability study are set forth in the following table, and show at theend of 3 weeks the preparation had lost 83.4% of its originalmicrobiological potency which is expressed in the mg. of tetracyclinepresent in an ml. of the liquid formulation.

Micro- Percent- Woeks at 37 C. biological age Potency, Initial rug/ml.

The aforementioned procedure was again followed using the sameformulation but substituting for tetracycline HCl, tetracycline neutral.The results of the stability study are set forth in the following table,and show that at the end of 3 weeks the preparation had lost 85.3% ofits original microbiological potency, which is expressed in the mg. oftetracycline present in an ml. of the liquid formulation.

Micro- Percent- Weeks at 37 C. biological age or Potency, Initialmg./Inl

Therefore, neither tetracycline or its acid addition salts are capableof forming aqueous propylene glycol formulations which are stable withregard to microbiological potency.

EXAMPLE III Stability of Tetracycline Metal Acid Complex in AqueousPropylene Glycol Solutions This example demonstrates that a physicallystable aqueous propylene glycol solution of tetracycline is obtained byusing the tetracycline metal acid complex.

A composition containing the following ingredients was prepared:

Tetracycline aluminum calcium gluconate complex (1:4:1:12) g 44.1Propylene glycol .....mL. 119 Sodium formaldehyde sulfoxylate mg 850Ethanolamine to pH 8.5. Water, q.s. ad ml.

The tetracycline complex was dissolved in approximately 30 ml. ofdistilled water with stirring. The sodium formaldehyde sulfoxylate wasdissolved in 2-3 ml. of distilled water and then added to theformulation. The pH of the solution was elevated to 8.5 withethanolamine and the volume was made up to 170 ml. with distilled water.Precipitation did not occur when this composition was diluted withcopious amounts of water.

The composition was then tested with regard to stability expressed inpotency. The following table, in which the figures represent quantitiesof tetracycline, demonstrates that aqueous propylene glycol solutions oftetracycline metal acid complex are stable with regard to potencyretention.

Initial potency:

Theoretical mg./ml 3 5 Actual mg./ml 38.2

2 months 4 months Room Temperature --mg./ml 37. 7 35. 6

42 C .mgJml. 34. 3

EXAMPLE IV Preparation of a Stable Solution of Tetracycline by in SituProduction of the Complex and Stability Thereof A composition containingthe following ingredients was prepared:

Tetracycline neutral (0.01 mole) 4.44 g. Aluminum isopropoxide (0.03mole) 6.12 g. Calcium oxide (0.01 mole) 0.56 g. Glucono-A-lactone (0.06mole) 10.68 g. Distilled water, 33 /3 32 ml.+make-up. Propylene glycol,66%% 64 ml. Sodium formaldehyde sulfoxylate,

Mono-ethanolamine, q.s. ad pH 8.5.

The aluminum isopropoxide and the glucono-A-lactone were added todistilled water and the mixture was then stirred overnight. Theresulting solution was filtered to remove traces of unreacted solids andthen distilled under vacuum to remove the isopropanol evolved during theformation of the aluminum guconate complex. After the isopropanol wasremoved, the volume of the aluminum gluconate solution was adjusted to32 ml. with distilled water to make up for the water that was removedwith the isopropanol during the vacuum distillation.

The tetracycline was then added to the above solution which was stirreduntil an essentially clear solution was obtained (approximately 30minutes). The calcium oxide was added and stirring continued forapproximately 3 hours until only traces of unreacted solids werepresent. The solution was then filtered and the propylene glycol wasadded slowly with stirring. The sodium formaldehyde sulfoxylate waspredissolved ,in a minimal amount of distilled water (approximately 1ml.) and then added to the formulation. The pH was then adjusted to 8.5with mono-ethanolamine and the formulation was filled into ampules at alevel of 2 mL/ampule. The ampules were then sealed under nitrogen.

The accelerated stability studies hereinabove set forth were repeated onthe solutions obtained by the aforementioned procedure. The stabilitystudies demonstrated a retention of potency over a sustained period oftime.

What is claimed is:

1. A stable liquid composition of tetracycline, suitable for parenteraladministration, comprising as a vehicle an aqueous solution containingfrom 30 to percent of a physiologically acceptable glycol, said vehiclehaving dissolved therein [from 10 to mg./ml. of a] tetracycline aluminumcalcium gluconate complex, containing 10 to 125 mg./ml. of tetracycline,and said composition having a pH of about 7.5 to 9.

2. The composition of claim 1 containing 0.5-1% of an antioxidant.

3. The composition of claim 2 in which the antioxidant is sodiumformaldehyde sulfoxylate.

4. The composition of claim 1 containing a base having a dissociationconstant greater than 10*.

5. The composition of claim 4 in which the base is monoethanolamine.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 2,736,725 2/1956 Ritter 424227 XR 2,944,541 7/1960Sacchi et al 424227 XR 2,984,686 5/1961 Blackwood et al. 424227 XR3,005,754 10/ 1961 Granatek 424227 3,009,956 11/1961 Noseworthy et al.260559 3,017,323 1/1962 Gordon et al. 424227 3,026,248 3/ 1962Noseworthy et al. 424227 3,053,892 9/1962 Sieger et al 424227 XR3,068,264 12/1962 Sieger et a1 424--227 XR LEWIS GOTIS, PrimaryExaminer.

S. K. ROSE, Assistant Examiner.

US. Cl. X.R.

